Antigenic responsiveness to allergens is imparted to mast cells and basophils by specific membrane binding of allergen binding IgE. Other cells have been shown to bind ligands non-randomly, especially to microvilli (dePetris, Nature 272: 66-68, 1978). Further, cell bound IgE has been shown to survive for prolonged periods of time on the cell surface (Isersky, Rivera, Mims, and Triche, J. Immunol. 122: 1926-1936, 1979). This study attempts to determine whether the prolonged survival is related to cellular re-distribution away from sites of active endocytosis; i.e., onto microvilli.